Normative factor structure of the AAMR adaptive behavior scale school second edition

Journal ofPsychoeducational Assessment 2002, 20, 337-345 NORMATIVE FACTOR STRUCTURE OF THE AAMR ADAPTIVE BEHAVIOR SCALE-SCHOOL, SECOND EDITION Marley W Watkins, Christina M Ravert, and Edward G Crosby The Pennsylvania State University The Adaptive Behavior Scale-School, Second Edition (ABS-S:2; Lambert, Nihira, & Leland, 1993) is one of the most popular tests of adaptive behavior Critical methodological flaws in the confirmatory factor analysis reported in the test manual and the results of independent exploratory factor analyses leave the structural validity of the ABS-S:2 underdefined The present study conducted exploratory factor analysis of the combined ABS-S:2 normative sample of 3,328 students (2,074 with mental retardation and 1,254 without mental retardation) Following principal axis factor extraction and oblique rotation, a two-factor solution was deemed the best dimensional model These results suggest that interpretation of the ABSS:2 should focus on its two major conceptual components (personal independence and social behavior) rather than the five factors and 16 domains endorsed by its authors Psychological constructs such as intelligence, self-esteem, and anxiety are an "attribute of people, assumed to be reflected in test performance" (Cronbach & Meehl, 1955, p 283) Because these unobservable constructs are abstracted from observed test performance, evidence must be educed to verify that test scores accurately reflect the intended constructs This process is called construct validation (Benson, 1998) and is integral to competent psychological assessment (American Educational Research Association, American Psychological Association, National Council on Measurement in Education, 1999) Valid measurement of the construct of adaptive behavior is especially important because it is central to the definition of mental retardation (APA, 1994) Adaptive behavior is a term that refers to a person's effectiveness in coping with daily environmental demands and must accompany subaverage general intellectual functioning to constitute mental retardation (Nihira, 1999) Unfortunately, there is little consensus regarding the dimensional structure of adaptive behavior (Thompson, McGrew, & Bruininks, 1999) For example, the Correspondence concerning this article should be addressed to Marley W Watkins, Department of Educational and School Psychology and Special Education, The Pennsylvania State University, 227 CEDAR Building, University Park, PA 16802 Electronic mail may be sent via Internet to mwwl0@psu.edu 338 WATKINS ET AL American Association on Mental Retardation (1992) published guidelines that delineate ten areas of adaptive behavior, but other experts have suggested that it is composed of one (Bruininks, McGrew, & Maruyama, 1988), five (Kamphaus, 1987), and seven (Meyers, Nihira, & Zetlin, 1979) dimensions McGrew and Bruininks (1989) reviewed the literature on the dimensionality of adaptive behavior and concluded that disparate results were related to the adaptive behavior test being analyzed and the type of analytic method used Given these confounds, it is important to scrutinize each test of adaptive behavior Of the 200 published instruments designed to measure adaptive behavior (Spreat, 1999), the Adaptive Behavior Scale-School, Second Edition (ABS-S:2; Lambert, Nihira, & Leland, 1993) is one of the most popular (Stinnett, Havey, & Oehler-Stinnett, 1994) Its dimensional structure was analyzed by confirmatory factor analysis (CFA) of 28 components extracted from the ABS-S:2 among the combined normative sample of 3,328 students Some components consisted of single items, whereas others contained two, three, or more items A five-factor model, corresponding to an a priori hypothesized structure, was selected by Lambert et (1993) based upon high componentfactor loadings Unfortunately, no alternative models were tested, loadings of components Ol1tO nonhypothesized factors were not reported, and model fit statistics were not provided These are critical methodological flaws (Kline, 1998; Thompson, 2000) that leave the structural validity of the ABS-S:2 underdefined Stinnett, Fuqua, and Coombs (1999) recognized this situation and applied exploratory factor analysis (EFA) to the ABS-S:2 normative sample However, correlation matrices were presented separately in the ABS-S:2 manual (Lambert et aI., 1993, p 51) for the sample of students with mental retardation and the sample of students without mental retardation Consequently, Stinnett et (1999) had to analyze and report factor analytic results separately for students with and without mental retardation rather than for the combined sample analyzed by Lambert et (1993) Results from both samples suggested a similar two-factor structure, and the authors concluded that there was no empirical support for the five-factor model advocated by Lambert et Such inconsistent construct validity results led Stinnett et (1999) to recommend continuing study of the dimensional structure of the ABS-S:2, especially among a general population comprised of students with and without mental retardation A combined sample was deemed desirable for two reasons First, psychologists typically use the ABS-S:2 with referral samples that contain students with and without mental retardation Thus, the combined sample consists "of people similar to those with whom the scale will be ultimately used" (Gorsuch, 1997, p 541) Second, sampling participants from the extremes of expected factors often produces clearer factors than would otherwise result (Gorsuch, 1988) Therefore, the present study conducted EFA analyses of the combined ABS-S:2 normative sample NORMATIVE FACTOR STRUCTURE OF THE AAMR ABS-S:2 339 METHOD Participants The ABS-S:2 normative sample of 3,328 students (2,074 with mental retardation and 1,254 without mental retardation) served as participants The separate correlation matrices for the 16 domain scores presented in the ABS-S:2 manual (Lambert et al., 1993, p 51) for students with and without mental retardation were pooled using the procedure specified by Becker (1996) This involved weighting each correlation coefficient by its degrees of freedom and then combining the weighted correlation matrices into a single matrix by summing the corresponding weighted coefficients and dividing this sum by the sum of the weighting factors Results are presented in Table Zeros were substituted·for unspecified nonsignificant entries in the original correlation matrices As noted by Stinnett et al (1999), this "was reasonable because the maximum nonsignificant TWas 04 for the MR group and 03 for the Non-MR sample" (p 35) Table Combined ABS-S:2 Correlation Matrix for 2,074 Students with Mental Retardation and 1,254 Students without Mental Retardation IF IF 1.0 PD 51 74 EA LD 80 NT 75 PV 55 SD 71 RE 73 SO 69 07 SB CO -.10 -.18 TR SHB -.24 SAB -.17 SE -.26 DIB -.02 PD EA LD NT 1.0 38 35 44 39 32 36 44 -.02 00 00 -.16 -.16 -.21 00 1.0 75 66 36 63 61 50 09 -.04 -.08 -.12 -.03 -.20 03 1.0 86 1.0 50 47 71 62 70 65 68 59 07 09 -.08 -.06 -.13 -.11 -.21 -.17 -.18 -.12 -.26 -.19 -.23 05 PV 1.0 67 64 61 -.12 -.37 -.32 -.29 -.24 -.24 -.21 SO SB CO TR SHB SD RE 1.0 76 76 02 -.30 -.26 -.32 -.24 -.38 -.16 1.0 74 1.0 -.03 -.07 1.0 -.30 -.30 49 1.0 -.30 -.30 40 70 1.0 59 57 1.0 -.30 -.36 34 67 -.23 -.28 26 45 51 10 34 30 45 -.29 -.39 -.10 -.18 48 45 54 51 SAB SE DIB 1.0 48 1.0 38 1.0 41 Note.-IF = Independent Functioning; PD = Physical Development; EA = Economic Activity; LD = Language Development; NT = Numbers and Time; PV = PrevocationalNocational Activity; SD = SelfDirection; RE = Responsibility; SO = Socialization; SB = Social Behavior; CO = Conformity; TR = Trustworthiness; SHB =Stereotyped and Hyperactive Behavior; SAB = Self-Abusive Behavior; SE =Social Engagement; DIB = Disturbing Interpersonal Behavior Instrument The ABS-S:2 is a major revision of the 1975 and 1981 Adaptive Behavior Scales Items were selected based on reliability and ability to discriminate among adaptive behavior levels (Lambert et al., 1993) The instrument is designed to assist in differential diagnosis of mental retardation, planning of special programs and treatment plans, and identification of relative adaptive 340 WATKINS ET AL strengths and weaknesses among individuals aged through 21 years The ABSS:2 was normed on 2,074 people with mental retardation from 40 states and 1,254 people without mental retardation from 44 states Additional data regarding the standardization sample and psychometrics of the ABS-S:2 are available in Lambert et al (1993) The ABS-S:2 is conceptually separated into two parts Part I focuses on personal independence and contains separate behavioral domains: Independent Functioning (IF), Physical Development (PD), Economic Activity (EA), Language Development (LD), Numbers and Time (NT), Prevocational/Vocational Activity (PV), Self-Direction (SD), Responsibility (RE), and Socialization (SO) Part II deals with social behavior and is divided into domains: Social Behavior (SB), Conformity (CO), Trustworthiness (TR) , Stereotyped and Hyperactive Behavior (SHB) , Self-Abusive Behavior (SAB) , Social Engagement (SE), and Disturbing Interpersonal Behavior (DIB) The scale yields scores for each of the 16 domains and five factors (personal self-sufficiency, community self-sufficiency, personal-social responsibility, social adjustment, and personal adjustment) Internal consistency reliability coefficients for the domain and factor scores ranged from 82 to 98 (Mdn = 905) and from 88 to 98 (Mdn = 945), respectively Analysis Given the lack of agreement concerning the dimensionality of the construct of adaptive behavior, the diverse results found with the ABS-S:2, and the atheoretical foundation of the ABS-S:2, EFA was deemed the most suitable analytic method As noted by Browne (2001), EFA is probably preferable to CFA under these conditions That is, lack of both theoretical and empirical congruence recommended an exploratory approach over a confirmatory method (Stinnett et aI., 1999) Domain scores served as dependent variables Principal axis factor extraction was selected to remove any assumptions about the distribution of the variables (Cudeck, 2000) Initial estimation of communalities was accomplished by placing squared multiple correlations on the diagonal Because determining the number of factors to retain for rotation is the most critical decision in EFA (Goodwin & Goodwin, 1999), the three most accurate methods identified by Velicer, Eaton, and Fava (2000) were applied: Parallel Analysis (PA; Horn, 1965), Minimum Average Partial Correlation (MAP; Velicer, 1976), and Scree (Cattell, 1966) Following the recommendation of Fabrigar, Wegener, MacCallum, and Strahan (1999), oblique rotation was preferred To reduce the probability of complex variables and ensure that only important loadings were interpreted (Hair, Anderson, Tatham, & Black, 1995), it was determined a priori that three salient structure coefficients of 2::.40 would be required to form a factor (Ford, MacCallum, & Tait, 1986) NORMATIVE FACTOR STRUCTURE OF THE AAMR ABS-S:2 341 RESULTS EFA was conducted with SPSS 10 for the Macintosh (SPSS, 2000) The correlation matrix was factorable, as indicated by the KMO measure of sampling adequacy (.65) and Bartlett's Test of Sphericity (p> 001) PA, MAP, and Scree procedures all indicated that two factors should be retained Following Oblimin rotation, both factors were saliently loaded by more than three variables (see Tables and 3) with no complex variables The factor intercorrelation was -.23 Thus, the two factors were relatively independent (John & BenetMartinez, 2000) Factor I accounted for 39% and Factor II for 18% of the variance Analysis ofnonredundant residuals found only ~ 1.101 Table Structure Coefficients for a Two-Factor Oblique Structure for the Adaptive Behavior Scale-School:2 Normative Sample of 3,328 Students Domain Factor I Factor II 90 49 76 89 83 65 84 84 80 -.14 -.08 -.02 -.15 -.06 -.38 -.33 -.31 -.37 05 -.19 -.21 -.29 -.22 -.33 -.10 52 79 78 78 67 49 67 Independent Functioning Physical Development Economic Activity Language Development Numbers and Time Prevoc/Vocational Activity Self-Direction Responsibility Socialization Social Behavior Conformity Trustworthiness Stereotyped/Hyperactive Behavior Self-Abusive Behavior Social Engagement Disturbing Interpersonal Behavior Communality 82 24 60 79 70 47 73 72 68 30 62 60 62 45 29 46 Note.-Salient structure coefficients (